This invention relates in general to solid state lasers and more particularly to temperature control of such lasers.
In a pumped solid state laser, a light source, such as a Gallium Arsenide diode array, is energized by an electrical power supply that may be switched on and off. Light from the light source energizes a lasing element (a laser slab, rod, or other geometry device composed of a material such as Nd:YAG) causing a laser light output.
The energy that is inputted to this laser assembly and that is not outputted as laser light must be absorbed or be transmitted from the assembly as heat. The energy that is absorbed increases the temperature of the laser assembly. The temperature rise in the laser assembly can cause catastrophic failure of materials if it is not maintained within limits. The temperature rise can also cause optical dimensions to change so that laser operation is degraded or will not occur.
Convection is the primary means of cooling present day solid state lasers. A fan forces gases or vapors over and through the light source and the lasing element. The light source and the lasing element are cooled by gases or vapors which pass out of the laser assembly as heated gases after absorbing heat from the light source and the lasing element. Laser operation during convection cooling is not possible in many cases. The flow of gases or vapors can interrupt light transmission along optical paths. Therefore, convection cooling has to occur between laser operations. The result is long cooling times and short laser operating times. These cooling problems limit many solid state lasers to low duty cycle operation.
It is therefore an object of this invention to cool a laser in a simpler and improved manner.
This and other objects of the invention are achieved by a liquid immersed pumped solid state lasing system and method. The lasing system comprises a light source and a lasing element spaced from the light source. The light source and the lasing element are mounted in an insulated container. A means is provided for inputting a clear cryogenic cooling liquid into the container to totally immerse the light source and the lasing element in the liquid. Heat transfer occurs by conduction from the light source and the lasing element to the liquid thereby cooling the light source and the lasing element to cryogenic temperatures. The container has a window for the output of laser light. A plurality of electrical leads which are superconducting at cryogenic temperatures are attached to the light source. When the leads are connected to a power supply outside the container, the light source directs light on the lasing element so that the lasing element is excited and transmits a light output through the window.
By wetting the surfaces of the light source and the lasing element with a liquid, heat transfer from the laser components is much greater than could be obtained in a solid to gas interface. Use of a boiling liquid coolant, such as liquid nitrogen, keeps thermal gradients low in the lasing system. This reduces mechanical stresses on the laser components so that the laser""s optical dimensions do not vary. Cooling at cryogenic temperatures increases the light output of light sources, such as GaAs diode arrays, in many cases, so that laser operation is more efficient. Cryogenic cooling permits the use of superconducting material for the power supply leads and interconnections within the matrix of GaAs diode light sources, resulting in a significant increase in laser efficiency and operational performance. Submersion of the diode arrays and the lasing element into the liquid cooling medium provides a laser of reduced complexity, reduced hardware requirements and reduced expense when compared to present techniques of cooling lasing systems of this type.
Additional advantages and features will become more apparent as the subject invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: